The present invention is directed to an apparatus for implantation into a bone in a patient""s spine or pelvis, and is particularly directed to an apparatus that, when implanted, is resistant to toggling in the bone and to being pulled from the bone. The present invention is also directed to an apparatus for attaching and stabilizing adjacent vertebral bodies while the vertebral bodies fuse together.
Bone screws are used in the medical field for a variety of purposes. Typical uses for bone screws, also referred as bone anchors, include treating a bone fracture, attaching a corrective device to parts of a fractured bone in an area adjacent to the fracture, and attaching a corrective device to a group of bones, such as vertebrae of a spinal column.
Most known bone screws use a conventional screw design, i.e. a solid shank, with one or more external thread convolutions. The solid shank and external threads of the conventional bone screws can cause the bone screws to displace an undesirably large amount of bone when implanted. Such conventional bone screws typically require a large amount of torque to implant the screw into a vertebral body. Furthermore, the resistance of the conventional screw to being pulled axially from the bone is dependent upon the surface area of the bone that interfaces with the screw threads.
It is also known to use a corkscrew-style helical spike as a tissue anchor. The known corkscrew-style tissue anchors, when implanted, displace less bone than the conventional bone screws, but are generally not able to withstand high tensile loads without structural failure. European Patent No. 0 374 088 A1 discloses a bone screw having a twin-corkscrew design.
One of the more challenging applications of a bone screw is implantation of the screw into the cancellous bone of a patient""s spine or pelvis. For example, bone screws are frequently implanted into the cancellous bone of a patient""s lumbar vertebrae during a spinal fixation procedure to correct scoliosis. Once implanted, the bone screws are used to mount suitable spinal fixation instrumentation, such as clamps, rods, and plates. Unfortunately, many of the known bonescrews, such as those described above, can be susceptible to toggling in the vertebral body and can also pull out of the vertebral body due to the substantial forces on the screws from human body movement and muscle memory. In order to achieve a high pull-out resistance, it is common to use additional screws, which results in an undesirably large amount of bone being displaced. In order to achieve a high pullout resistance, it is also known to thread a bone screw all of the way through a vertebrae and place a nut on the opposite side. However, use of such a nut increases the complexity of the surgical procedure.
Hence, it is desirable to provide an apparatus for implantation into a bone in a patient""s spine or pelvis in a minimally invasive endoscopic procedure with a reduced amount of insertion torque required. The desirable apparatus would provide a platform for connecting spinal fixation instrumentation and, when implanted, be highly resistant to toggling in the bone and to being pulled out of the bone despite the substantial forces on the apparatus from human body movement and muscle memory.
Another application for an anchor or fastening-type apparatus in the field of spine surgery is the stabilization of adjacent vertebrae. Each adjacent pair of vertebrae in the human spinal column are separated by an intervertebral disc that makes relative movement of the vertebrae possible. Problems, however, can develop with one or more of the discs, causing severe back pain. In some cases, it is necessary to remove a problematic disc and to fuse the adjacent vertebrae together in order to relieve pain.
One known method for fusing an adjacent pair of vertebrae following removal of a disc is to implant a device, commonly referred to as a fusion cage, into the interbody space where the disc was removed. The fusion cage facilitates fusion of the vertebrae. Typically, procedures such as reaming and/or tapping of adjacent vertebrae are required to prepare the adjacent vertebrae to receive the fusion cage. Such procedures normally involve substantial cutting of the hard cortical bone of the end plates of the adjacent vertebrae, which can weaken the end plates and lead to collapse of the vertebrae. The fusion cage is then positioned in the interbody space and into engagement with the adjacent vertebrae. At least one known fusion cage has relatively movable parts that enable the fusion cage to be expanded after the fusion cage is positioned in the interbody space between adjacent vertebrae. The design of this expandable fusion cage is, however, relatively complex.
Typically, a fusion cage includes an internal cavity that is filled with bone graft material. The fusion cage and the bone graft material promote bone growth that slowly unites the adjacent vertebrae. The typical fusion cage, while in engagement with the adjacent vertebrae, does not attach to the vertebrae and thus does not resist relative movement of the vertebrae, through bending or rotation, along any one of the three planes of motion (sagittal, coronal, or horizontal). Rather, the typical fusion cage relies on the viscoelasticity of the surrounding ligaments to stabilize the adjacent vertebrae.
It is desirable to provide an apparatus for implantation into an adjacent pair of vertebral bodies that attaches to and thus fastens the vertebral bodies while they fuse together despite the forces on the apparatus from human body movement and muscle memory. It is further desirable to provide an apparatus which has a reduced insertion torque requirement, a simple one-piece construction, and which may be implanted into an adjacent pair of vertebrae without having to prepare the adjacent vertebrae to accept the apparatus by substantial cutting of the cortical bone.
The present invention is an apparatus for implantation into a bone in a patient""s spine or pelvis. The apparatus, when implanted, is resistant to toggling in the bone and to being pulled from the bone. The apparatus comprises a platform for engaging a bone in a patient""s spine or pelvis. The platform includes structure for connection to a spinal fixation implant. The apparatus further comprises at least one helical spike for embedding into the bone upon rotation of the platform. The at least one helical spike projects tangentially from the platform and extends around a longitudinal axis. The at least one helical spike has a tip portion at a distal end which penetrates into the bone as the platform is rotated. The at least one helical spike, when implanted, has a conical shape that increases in diameter as the at least one helical spike extends away from the platform.
In accordance with one feature of the present invention, the at least one helical spike has a first condition in which the at least one helical spike has a first maximum diameter and a second condition in which at least a portion of the at least one helical spike expands to a second maximum diameter that is larger than the first maximum diameter.
In accordance with another feature of the present invention, the at least one helical spike has a first axial length in the first condition and a second axial length in the second condition, the second axial length being smaller than the first axial length.
In accordance with yet another feature of the present invention, at least a portion of the at least one helical spike is made of a shape memory alloy that is responsive to changes in temperature above and below a predetermined temperature transition range, the at least one helical spike being in the first condition when the temperature of the at least one helical spike is below the predetermined temperature transition range, the at least one helical spike being in the second condition when heated above the predetermined temperature transition range, the at least one helical spike being implanted into the bone in the second condition.
In accordance with another embodiment, the present invention is an apparatus comprising at least one anchor for implantation into a bone. The anchor, when implanted, is resistant to toggling in the bone and to being pulled from the bone. The apparatus further comprises a spinal fixation implant for extending between and connecting a plurality of bones. The anchor includes a platform having a first surface for facing the bone. The platform further has structure for connection with the spinal fixation implant. The anchor further includes at least two helical spikes for embedding into the bone upon rotation of the platform. The at least two helical spikes are spaced apart and project tangentially from the first surface on the platform. The at least two helical spikes extend around a longitudinal axis. Each of the at least two helical spikes has a tip portion at a distal end which penetrates into the bone as the platform is rotated. The at least two helical spikes, when implanted, have a conical shape that increases as the at least two helical spikes extend away from the platform.
In accordance with yet another embodiment, the present invention is an apparatus for implanting an anchor into a bone in a patient""s spine or pelvis. The apparatus comprises an anchor having a platform and at least one helical spike for embedding into the bone upon rotation of the platform. The platform faces a bone in a patient""s spine or pelvis and includes structure for connection to a spinal fixation implant. The at least one helical spike projects tangentially from the platform and extends around a longitudinal axis. The at least one helical spike has a tip portion at a distal end which penetrates into the bone as the platform is rotated. The at least one helical spike has a first condition in which the at least one helical spike has a first maximum diameter and a second condition in which at least a portion of the at least one helical spike expands to a second maximum diameter that is larger than the first maximum diameter. The anchor, when implanted, is resistant to toggling in the bone and to being pulled from the bone.
In accordance with a feature of the present invention, the apparatus further comprises a tubular sleeve for receiving the anchor. The tubular sleeve has an inside diameter that is approximately equal to the first maximum diameter of the at least one helical spike of the anchor. The anchor is positionable inside the tubular sleeve when in the first condition.
In accordance with still another embodiment, the present invention comprises an apparatus for implantation into an adjacent pair of vertebral bodies having first and second surfaces that oppose each other. The apparatus, when implanted, is attached to the adjacent pair of vertebral bodies and stabilizes the vertebral bodies while the vertebral bodies fuse together. The apparatus comprises a platform having a third surface extending transverse to the first and second surfaces. The apparatus further comprises at least one helical spike for embedding into each of the adjacent pair of vertebral bodies upon rotation of the platform to attach the at least one helical spike to each of the vertebral bodies and thus fasten (pin) the vertebral bodies together. The at least one helical spike projects from the platform and extends around a longitudinal axis. The at least one helical spike has a tip portion at a distal end for penetrating the first and second surfaces and for screwing into the adjacent pair of vertebral bodies as the platform is rotated. The at least one helical spike at least partially defines an internal cavity for receiving material that promotes fusion of the vertebral bodies. The at least one helical spike, when implanted, has a conical shape that increases in diameter as the at least one helical spike extends away from the platform.